I haven't used Google's previous implementations, and I'm bummed I still can't use this one. I have high hopes for this implementation because it is written to comply with the W3C Payment Request API (https://www.w3.org/TR/payment-request/). Microsoft and Mozilla are also working on implementations. Apple Pay for Web follows a very similar API. As a developer who deals with payments this makes my life a lot easier as I can create a single implementation that enables users of almost every major browser to take advantage of speedy checkout.